LLM-as-judge default config triggers google-genai's AFC warning in every eval run

[roanny]

Summary

Every rubric-based eval run logs this google-genai warning once per process:

WARNING google_genai.models: Direct use of automatic function calling (AFC) in AsyncModels.generate_content is not recommended. Instead, we recommend to use AFC in AsyncChat.send_message. Similarly, direct use of AFC in AsyncModels.generate_content_stream is not recommended. ...

The agent under evaluation does not cause it. It comes from the LLM-as-judge request.

Where it comes from

LlmAsJudge builds the judge request with config=self._judge_model_options.judge_model_config or genai_types.GenerateContentConfig() (src/google/adk/evaluation/llm_as_judge.py:224-225 on main at ce53a36c0a, and the same in 2.9.0 and 2.9.1).

That default config sets neither tools nor automatic_function_calling. google-genai's AsyncModels.generate_content therefore takes its AFC branch and logs the warning:

• _extra_utils.should_disable_afc returns False when automatic_function_calling is unset.
• With no tools there are no AFC-incompatible tool indexes, so the direct _generate_content path is skipped.

An agent's own model calls do not hit this. ADK sends tools as function_declarations, which google-genai marks AFC-incompatible, so those calls go straight to _generate_content.

How it was observed

In an eval suite running rubric_based_*_quality_v1 metrics with gemini-3.5-flash as judge (google-adk 2.9.0, google-genai as resolved by it):

• The warning appears once per pytest process.
• It always appears right after the agent's inference for the case ends and right before the rubric verdicts.
• It never appears during the agent's own model calls.
• The deployed agent's logs, same code without the eval harness, contain no occurrence over 7 days.

Suggestion

The judge never needs automatic function calling. Its default config could disable it explicitly:

config=self._judge_model_options.judge_model_config
or genai_types.GenerateContentConfig(
    automatic_function_calling=genai_types.AutomaticFunctionCallingConfig(disable=True)
),

This does not change the request sent to the model (the field is client-side only) and removes a warning that points users at their own agent. Users who pass judge_model_config are unaffected.

[chelsealong]

Picking this one up now — opening a PR shortly. Flagging it here so nobody duplicates the work; if someone is already on it, say so and I will drop mine.